Nghiên cứu các chiến lược đảm bảo chất lượng dịch vụ (QoS) trong các mạng không dây

1

ĐẠI HỌC QUỐC GIA HÀ NỘI
TRƯỜNG ĐẠI HỌC CÔNG NGHỆ


Hà Minh Toản

NGHIÊN CỨU CÁC CHIẾN LƯỢC
ĐẢM BẢO CHẤT LƯỢNG DỊCH VỤ (QoS)
TRONG CÁC MẠNG KHÔNG DÂY



Ngành: Công Nghệ Thông Tin
Chuyên ngành: Truyền dư
̃
liê
̣
u va
̀
ma
̣
ng ma
́
y tnh
Mã số: 60 48 15


LUẬN VĂN THẠC SĨ

NGƯỜI HƯỚNG DẪN KHOA HỌC:
PGS. TS. Nguyễn Đình Việt




HÀ NỘI – 2008

2

MỤC LỤC

DANH MỤC CÁC KÝ HIỆU, CÁC CHỮ VIẾT TẮT 4
DANH MỤC CÁC HÌNH VẼ 6
DANH MỤC CÁC BẢNG 8
GIỚI THIỆU CHUNG 9
CHƢƠNG I. CHẤT LƢỢNG VÀ YÊU CẦU CHẤT LƢỢNG DỊCH VỤ (QoS) . 11
 13
 15
 16
 18
 19
CHƢƠNG II. CHUẨN MẠNG LAN KHÔNG DÂY IEEE 802.11 20
 20
-based network) 20
-hoc 22
 22
 24
 26
 32

 32
CHƢƠNG III. ĐẢM BẢO QoS TRONG CƠ CHẾ EDCA IEEE 802.11e 33
- EDCA 34
 34
- EDCAF 35
 36
 40
 45
CHƢƠNG IV. MÔ PHỎNG VÀ PHÂN TÍCH KẾT QUẢ 46
NS-2 47

3

- 48
 48
 49
 50
 53
 55
 55
 63
KẾT LUẬN VÀ HƢỚNG NGHIÊN CỨU TIẾP THEO 67
 67
 68
TÀI LIỆU THAM KHẢO 69


4

DANH MỤC CÁC KÝ HIỆU, CÁC CHỮ VIẾT TẮT




QoS
Quality of Service

LAN
Local Area Network

WLAN
Wireless Local Area Network
c b không dây
IEEE
Institute of Electrical and
Electronics Engineers
 
t
DCF
Distributed Coordination
Function

PCF
Point Coordination Function

DIFS
DCF Interframe Space

frame DCF
SIFS
Short Interframe Space













trong IEEE 802.11



CSMA/CA
Carrier Sense Multiple Access
with Collision Avoidance

















RTS
Request To Send



802.11
CTS
Clear To Send


g 
truyn trong IEEE 802.11

5

HCF
Hybrid Coordination Function

EDCA
Enhanced Distributed Channel
Access


HCCA
HCF Controlled Channel Access

C
trung
EDCAF
Enhanced Distributed Channel
Access Function


AIFS
Arbitration Interframe Space



toán quay lui trong EDCAF
TXOP
Transmission Opportunity

NS-2
Network Simulator version 2








2
CBR
Constant Bit Rate












(



-2)
UDP
User Datagram Protocol












TCP

Transmission Control Protocol




giao 

.

6

DANH MỤC CÁC HÌNH VẼ
 21
-hoc 22
 23
 23
 24
Hình  25
 27
 28
 28
 29
 30
 35
 37
Hình 3.3: Contention Free Bursting (CFB) 40
 41
 42
hông tin QoS. 43
 44

 44
-2 47
Hình 4.2a: 


























. 57

7

Hình 4.2b: 



























m không dây 57
Hình 4.3: 



  





























 


. 59
Hình 4.4: 



  




































không dây. 60
Hình 4.5: 



  

























 


. 61
Hình 4.6: 



  



















 



















. 62
 63
Hình 4.8: 





. 64
Hình 4.9: 

  






. 65


8

DANH MỤC CÁC BẢNG
 34
. 36

 38
 64


9

GIỚI THIỆU CHUNG
Internet ngày nay cho 
Nó
,  thông tin nhanh chóng và  t, giúp nâng cao
,  và công ty

 Internet, các  
 




 
                 
N     


     
 










“Nghiên cứu các chiến lược đảm bảo chất lượng dịch vụ (QoS) trong
các mạng không dây” c
 Chương I:              

các

10



 dây;

 Chương II:             
802.11  
. Chúng ta 
DCF (Distributed Coordination Function)
     PCF (Point Coordination Function). 

, 















 a






 



















.
 Chương III: 

 
cao (Enhanced Distributed Channel Access - EDCA) 
lai (Hybrid Coordination Function - HCF)    Cùng
 
  

 Chương IV: 
-






 , 



  


 k 








 LAN không
dây IEEE 802.11; c









 







 
EDCA 



  802.11e; 























.
 Chương V: 








 . 

t


11

CHƢƠNG I. CHẤT LƢỢNG VÀ YÊU CẦU CHẤT LƢỢNG DỊCH VỤ
(QoS)
ARPANET â  nay,      
      p   cao DARPA (Defense Advanced
Research Projects Agency)  vào , 
hình datagram). T
m

         
hau. Ban
  
    , e-     
datagram , Internet
cung các   best-effort  - l
p, không nào cho
các . Khi 
hàng uter 
cho 
gói tin, nên 
 Dbest-effort 
, rõ ràng là nó không 


 Chính vì               
nguyên cho 
 
Vào      i v     
Telecommunication Union - mô hình i là c
(Asynchronous Transfer Mode - ATM) cho 
       B-ISDN (Broadband-Integrated Service Digital
 

kênh,  
khá
 
trong 

12

  
 

. Chính Web ,
          c       
H

       , VoIP,    , P2P (peer-to-
peer
   

datagram 

có 



không  là  
, tr


c(Quality of Service  QoS) Internet
d tài nguyên
(latency),
(jitter), (loss
sàng d

cd


các hd
.
 cd

theo  c
d

13

 
cd là  
cd
phân loại các dòng lưu lượng, 
các cơ chế quản lý bộ nhớ đệm (buffer) và các thuật toán lập lịch gói tin. Nhìn chung,
   c  d          

.
ccd 
Internet.  các gói tin
 (router) Các tvà phát
. Trong hai 
t 
c(processor sharing- PS).
c
    g max-        
; (misbehave);
 - 
 
-in first-out (FIFO) ( first-
come first-serve - FCFS)          andom Early
Detection (RED).V pháp d
d(Integrated services - Intserv), d  (Differentiated
services - Diffserv)



. 4/ M


I.1. Đại lƣợng cần đảm bảo chất lƣợng dịch vụ
 cho  
 chính sau :
1. Băng thông: 
trong m 

14

khác :  (data rate), 
  thông (transmission rate), c  bit (bit rate) hay  

hay 
   

hình cho nhóm này là streaming media, Internet telephony hay VoIP và video

tác  .
       
        

  thiên  . 
này    email,  file, web và tin

giây. 
 
 
2. Độ trễ:  (VoIP),
 hình (video conferencing)(Virtual Reality), và game
online 
     ng này.  
- , khi 
khi 

 (transmission)
(propagation)
 
  

8 microsecond  s
(p
 
sáng là 3x10
8

trong hàng 
 ch
Ccho
- 

15

. d
150 mili giây

3. Thăng giáng độ trễ: 
 
ph 
 
 
 
 (buffer) 
 
 

 


4. Tỉ lệ mất mát dữ liệu: C nhìn chung 

 , chúng có
cthoát 
       

, web thông  .


I.2. Những ứng dụng yêu cầu đảm bảo chất lƣợng dịch vụ

nh.
, và có 

 tqua

                
                -



16

 

            -   
   







 







     





I.3. Cơ chế đảm bảo dịch vụ trong mạng có dây

 Ts
              . M   
router, chính
, 

 . M
 
n multi-path routing). 


17

có hop) 

cùng lúc hay theo  .


Trong vài   
               tài
                tài
u l 

            
- 
            
  â              

d
dành riêng ngay

-
dành tài
nguyên trên 
dành 



 
controlled-

 
.
               
Edge router


                
router 


18


-effort thông th

cho 
 

               
chính xác.
I.4. Vấn đề phát sinh khi đảm bảo chất lƣợng dịch vụ cho mạng không dây.
          
 
không dây. H 
phát sinh làm cho 
ông dây.
  khi    
,

 c truyn không dây và tính 
tr  (Hidden terminal), tr l (Exposed Terminal), tín hi
truy theo nhi  (multi-path propagation) 
ông dây [1].
   
-lô-mé



Metropolitan Area Networks - MANs), và nó là

          
ad-hoc 
phép 
p
. 
 
(L
quá trình 

19

, 
).
       
.  dành

. là không 

  
 

I.5. Sự tiếp nhận của ngƣời sử dụng về chất lƣợng dịch vụ
  cchính là 
 . dành
cho  
. Ngoài ra, 


xem xét hi sinh  
có 
nào       
            mong
 
            o    
 ph
cph


               
                 



20

CHƢƠNG II. CHUẨN MẠNG LAN KHÔNG DÂY IEEE 802.11
IEEE 802.11 MAC, 
 t 
  
 n tán - DCF (Distributed Coordination
 PCF (Point
 không 

   không  Trong 
tôi trình bày 
 QoS.
II.1. Cấu trúc hệ thống mạng WLAN

               (infrastructure-
based) -hai 

khô
 .m không
dây.
II.1.1. Mạng có cơ sở hạ tầng (Infrastructure-based network)
 
 
 chung AP (Access Point). Các 
 mà thông qua AP. Hình 2.1 minh ho mt m 

21


Hình 2.1: Mạng không dây có cơ sở hạ tầng
 c :
 AP không 
.
 

 

  
 
 
    và sau           


 truy 

             m  


22


k1, 2, 5].
II.1.2. Mạng Ad-hoc
Ad-    d trên 
m có dây  
 Các  -
c nhau
(vùng mà các         
. Chính vì
-

 
hidden terminal) hay exposed terminal),
 [1, 5]. Tuy nhiên, chính
-

        
-hoc.

Hình 2.2: Mạng không dây ad-hoc
II.2. Kiến trúc giao thức
ang  s d ph bi cho
2.3 mô hình 





2.3, trên

23

con c  LLC (Logical Link Control) có
con 
           môi tr 


      -network Access Protocol - SNAP) và các công


Hình 2.3: Cấu trúc chuẩn IEEE 802.11 và cầu nối
mô 

 - PLCP) và thành
      -    
hình 2.4
- CCA 
- ng
 sóng mang
 [1, 5]. Chúng


Hình 2.4: Tầng giao thức trong chuẩn IEEE 802.11

24

II.2.1. Tầng vật lý



         

t 
, 5].
II.2.1.1 Kĩ thuật trải phổ nhảy tần FHSS (Frequency Hopping Spread Spectrum) [1,
5, 4]
s d
chung m d tn s 


kênh n


tin -
GFSK (Gaussian shaped Frequency Shift Keying) 

Hình 2.5: Định dạng của một frame quy định trong FHSS 802.11 PHY
Hình 2.5 
PLCP preamble)
 PLCP 
               

7
+z
4



 Sự đồng bộ hóa (Synchronization):  
bit theo m 


25

 Đoạn phân cách đầu frame SFD (Start Frame Delimiter):    
pattern là 0000
sau tr synchronization  .
 Độ dài PLW (PLCF_DPU Length Word):  con  tr
PLCP header,  
 payload. 
 Trường PSF (PLCP Signalling): 

 Trường kiểm tra lỗi Header - HEC (Header Error Check): 
   -  
 sinh G(x) = x
16
+x
12
+x
5
+1.
II.2.1.2 Kĩ thuật trải phổ điều khiển tuần tự DSSS [1, 5, 4]
DSSS ,   t trong IEEE
8002.11, theo phng pháp này- 
      
không b ng (multi-path propagation).
Theo chu IEEE 802.11, 



7
+z
4


Hình 2.6: Định dạng của một frame quy định trong DSSS 802.11
2.6, bao
            

 Trường đồng bộ hóa (Synchronization): dài 

sóng mang (cho CCA).
 Đoạn phân cách đầu frame SFD (Start Frame Delimiter): dài 16 bit có 
